Wall Street banks face heightened scrutiny from the Commodity Futures Trading Commission (CFTC) over their latest tactic to escape U.S. trading rules for overseas derivatives.

The regulator sent letters yesterday to JPMorgan Chase & Co., Goldman Sachs Group Inc., Bank of America Corp., Citigroup Inc., and Morgan Stanley seeking further information about the practice of removing parent-company guarantees from overseas trades. An agency official, who asked not to be named because the letters aren't public, confirmed that they were sent to the banks.

"I want to ask some more questions and understand exactly what they've done—what's been the effect on price, credit standing, ratings, and so forth, what disclosures have been made. So we're doing that," Timothy Massad, the agency's chairman, said today at an event hosted by Politico. "We'll see what we get from that and then decide what actions to take."